Wednesday, January 26, 2011

The Sins Against the Fathers (and the Mothers)

Researchers at the University of Texas at Austin and the University of Virginia looked at 750 pairs of American twins who were given a test of mental ability at the age of 10 months and then again at the age of 2. By studying the performance of identical versus fraternal twins, the scientists could tease out the relative importance of factors such as genetics and the home environment. Because the infants came from households across the socioeconomic spectrum, it also was possible to see how wealth influenced test scores.

When it came to the mental ability of 10-month-olds, the home environment was the key variable, across every socioeconomic class. But results for the 2-year-olds were dramatically different. In children from poorer households, the choices of parents still mattered. In fact, the researchers estimated that the home environment accounted for approximately 80% of the individual variance in mental ability among poor 2-year-olds. The effect of genetics was negligible.

The opposite pattern appeared in 2-year-olds from wealthy households. For these kids, genetics primarily determined performance, accounting for nearly 50% of all variation in mental ability. (The scientists made this conclusion based on the fact that identical twins performed much more similarly than fraternal twins.) The home environment was a distant second. For parents, the correlation appears to be clear: As wealth increases, the choices of adults play a much smaller role in determining the mental ability of their children.

Children from wealthy households get all the advantages that money can buy, from music lessons to SAT tutors. Although parents might fret over the details of such advantages—is it better to play the piano or the violin?—these details are mostly insignificant, subject to the law of diminishing returns. As the science blogger Razib Kahn notes, "When you remove the environmental variance, the genetic variance remains."

These results capture the stunning developmental inequalities that set in almost immediately, so that even the mental ability of 2-year-olds can be profoundly affected by the socio-economic status of their parents. As a result, their genetic potential is held back.

Single inductive studies should be treated with great caution, especially in politically-charged subjects, but this study is rather more evidence for than against the notion that you don't need to use anything like the alcohol-poisoning of fetuses depicted in Brave New World to neurologically impair and engineer an underclass.